Bone fastener assembly

ABSTRACT

The present invention provides a bone fastener assembly useful in constructs for stabilizing bones of a patient. In one aspect of the invention, a bone fastener assembly includes a connecting member, a fastener seat, and a bone fastener. The fastener seat and fastener are receivable in the connecting member and the fastener seat is movable from a first position to a second position to retain the fastener in the connecting member. In another aspect of the invention, a bone fastener assembly includes a rod holder, a fastener seat mounted to the rod holder for rotation about the rod holder axis; and a bone, fastener. The bone fastener is generally “T”-shaped and engages the fastener seat in pivoting relationship such that the bone fastener is able to pivot to vary the angle between the bone fastener and the fastener seat.

FIELD OF THE INVENTION

The invention relates to medical fixation devices and more particularlyto bone fastener assemblies useful in constructs for stabilizing bonesof a patient.

BACKGROUND

A variety of orthopedic and neurological procedures make use offasteners in constructs connecting one bone, or bone fragment, toanother. For example, the connection of one vertebra of the human spineto another vertebra is a common beneficial procedure. The vertebrae ofthe human spine are arranged in a column with one vertebra on top of thenext. An intervertebral disc lies between adjacent vertebrae to transmitforce between the adjacent vertebrae and provide a cushion between them.The discs allow the spine to flex and twist.

With age, spinal discs begin to break down, or degenerate resulting inthe loss, of fluid in the discs and consequently resulting in thembecoming less flexible. Likewise, the disks become thinner allowing thevertebrae to move closer together. Degeneration may also result in tearsor cracks in the outer layer, or annulus, of the disc. The disc maybegin to bulge outwardly. In more severe cases, the inner material ofthe disc, or nucleus, may actually extrude out of the disc.

In a process known as spinal stenosis, the spinal canal may narrow dueto excessive bone growth, thickening of tissue in the canal (such asligamentous material), or both.

The facet joints between adjacent vertebrae may degenerate and causelocalized and/or radiating pain.

In addition to degenerative changes in the disc, the spine may undergochanges due to trauma from automobile accidents, falls, heavy lifting,and other activities.

The spine may also be malformed from birth or become malformed over timesuch as for example in cases of scoliosis, kyphosis, spondylosis,spondylolisthesis, and other deformities.

The conditions described above can result in disfigurement, pain,numbness, weakness, or even paralysis in various parts of the body. Allof the above conditions and similar conditions are collectively,referred to herein as spine disease.

Typically, surgeons treat spine disease by attempting to stabilizeadjacent vertebrae relative to one another and/or restore the normal,spacing between adjacent vertebrae to improve the shape of the spine andto relieve pressure on affected nerve tissue. Stabilizing the vertebraeis often accomplished with plates and/or rods attached to the vertebraewith fasteners such as screws such as for example pedicle screws. Thestabilization may be rigid such that it eliminates motion betweenadjacent vertebrae and encourages bony fusion between the vertebrae orit may be dynamic to allow continued motion between the vertebrae.Often, the stabilization includes inserting a rigid spacer made of bone,metal, or plastic into the disc space between the adjacent vertebrae andallowing the vertebrae to grow together, or fuse, into a single piece ofbone.

The patients anatomy and/or the desired correction frequently requirealigning the fastener at various angles relative to the bone and therest of the stabilizing construct. Screws have been developed that areable to be angled relative to the stabilizing construct and they aretypically referred to as “polyaxial” screws. However, despite the factthat numerous such polyaxial screw systems have been marketed,improvements are desirable. In particular, current devices providelimited angular adjustment.

SUMMARY

The present invention provides a bone fastener assembly useful inconstructs for stabilizing bones of a patient.

In one aspect of the invention, a bone fastener assembly includes aconnecting member, a fastener seat, and a bone fastener. The fastenerseat and fastener are receivable in the connecting member and thefastener seat is movable from a first position to a second position toretain the fastener in the connecting member.

In another aspect of the invention, a bone fastener assembly includes arod holder, a fastener seat mounted to the rod holder for rotation aboutthe rod holder axis; and a bone fastener. The bone fastener is generally“T”-shaped and engages the fastener seat in pivoting relationship suchthat the bone fastener is able to pivot to vary the angle between thebone fastener and fastener seat.

In another aspect of the invention, the rod holder and fastener seateach include an annular rim and the bone fastener assembly furtherincludes a swivel ring having an internal diameter and an annular grooveformed about the internal diameter simultaneously engageable with theannular rims of the rod holder and the fastener seat.

In another aspect of the invention, the rod holder and fastener seateach comprise a rim and an undercut and the rod holder and fastener seatare engageable with one another in snap-fitting relationship with therim of one fitting into the undercut of the other.

In another aspect of the invention, the fastener seat and the rod holdereach include a groove and the fastener seat and rod holder telescopetogether with the grooves aligned. The bone fastener assembly furtherincludes a locking ring sized to seat simultaneously in both grooves andlock the fastener seat and rod holder together.

In another aspect of the invention, the bone fastener assembly includesat least one plate mountable to the rod holder and engageable with thefastener seat.

In another aspect of the invention, the head of the fastener includes aseparate member mounted to the fastener for rotation about the fasteneraxis.

In another aspect of the invention, the head of the fastener includesfirst and second ends and an annular groove formed about each of thefirst and second ends. Each annular groove receives a portion of thefastener seat on opposing sides of the fastener seat.

BRIEF DESCRIPTION OF THE DRAWINGS

Various examples of the present invention will be discussed withreference to the appended drawings. These drawings depict onlyillustrative examples of the invention and are not to be consideredlimiting of its scope.

FIG. 1 is a perspective view of a bone fastener assembly according tothe present invention;

FIG. 2 is a side elevation view of the bone fastener assembly of FIG. 1;

FIG. 3 is a bottom plan view of the bone fastener assembly of FIG. 1;

FIG. 4 is an exploded perspective view of the bone fastener assembly ofFIG. 1;

FIG. 5 is a side sectional view of the bone fastener assembly of FIG. 1;

FIG. 6 is a side sectional view of the bone fastener assembly of FIG. 1;

FIG. 7 is a side sectional view of the bone fastener assembly of FIG. 1;

FIG. 8 is a side sectional view of the bone fastener assembly of FIG. 1;

FIG. 9 is a side sectional view of the bone fastener assembly of FIG. 1illustrating an alternative fit of the parts;

FIG. 10 is a top plan view of an alternative arrangement for the screwseat of FIG. 1;

FIG. 11 is a partial side sectional view of the screw seat of FIG. 10;

FIG. 12 is a side sectional view of the screw seat of FIG. 10;

FIG. 13 is an exploded perspective view of another embodiment of a bonefastener assembly according to the present invention;

FIG. 14 is a partial side sectional view of the bone fastener assemblyof FIG. 13;

FIG. 15 is a side sectional view of the bone fastener assembly of FIG.13;

FIG. 16 is an exploded perspective view of another embodiment of a honefastener assembly according to the present invention;

FIG. 17 is a side sectional view of the bone fastener assembly of FIG.16;

FIG. 18 is a detail view of the side sectional view of FIG. 17;

FIG. 19 is an exploded perspective view of an alternative arrangementfor the bone screw of FIGS. 13-17;

FIG. 20 is a side sectional view of the embodiment of the bone screw ofFIG. 19;

FIG. 21 is an exploded perspective view of another embodiment of a bonefastener assembly according to the present invention;

FIG. 22 is a top sectional view of the bone fastener assembly of FIG.21;

FIG. 23 is aside sectional view of the bone fastener assembly of FIG.21;

FIG. 24 is an exploded perspective view of another embodiment of a bonefastener assembly according to the present invention;

FIG. 25 is side sectional view of the bone fastener assembly of FIG. 24;

FIG. 26 is an exploded perspective view of another embodiment of a bonefastener assembly according to the present invention; and

FIG. 27 is side sectional view of the bone fastener assembly of FIG. 26.

DESCRIPTION OF THE ILLUSTRATIVE EXAMPLES

Embodiments of a bone fastener assembly according to the presentinvention include a bone fastener and a connecting member mountedtogether to permit the fastener to pivot relative to a longitudinal axisof the assembly and swivel about the longitudinal axis. The fastener andconnecting member mounting may be biased to permit a greater degree ofpivoting of the fastener in one direction relative to the connectingmember of they may be constrained to permit pivoting in only onedirection. By biasing or selectively constraining the pivoting aspect ofthe fastener relative to the connecting member both the amount ofpivoting in the preferential direction and the strength of the mountingmay be increased. Due to the swiveling nature of the mounting betweenthe fastener and connecting member, the maximum pivot position of thefastener relative to the connecting member may be oriented independentlyat any swivel position about the longitudinal axis of the assembly. Thisarrangement is therefore geometrically comprehensive with respect to therelative orientation of the fastener and connecting member.

The bone fastener may include a screw, pin, nail, bolt, staple, hook,and/or any other suitable fastener for engaging a bone.

The connecting member may include a plate engaging stud, rod holder,and/or any other suitable member for assembling a construct forstabilizing bones of a patient.

The mounting may include a ball and socket, hinge, spindle, and/or othersuitable mountings.

While the specific embodiments used to illustrate the invention show thebone fastener assembly in the form of a pedicle screw useful to attach arod to a vertebrae, the bone fastener assembly may connect to a bone inany of the variety of ways known in the art and may be utilized in anyof the variety of constructs known in the art to stabilize bones at anylocation within the body.

For example, FIGS. 1-3 illustrate a pair of bone fastener assemblies inthe form of pedicle screw assemblies 100 coupled to a spinal rod 102 inorder to fix adjacent vertebrae relative to the rod 102 and therebystabilize the vertebrae relative to one another. Each pedicle screwassembly 100 includes a bone fastener in the form of a screw 104, aconnecting member in the form of a rod holder 106, and a mounting in theform of a screw seat 108 (FIG. 2) linking the screw 104 and rod holder106. The assembly includes a longitudinal axis 110 through the rodholder 106, screw seat 108, and screw 104.

As best seen in FIG. 2, the screw 104 is able to pivot in at least onevertical plane containing the longitudinal axis 110 to vary the anglebetween the screw 104 and rod holder 106. The screw seat 108 permits thescrew 104 to pivot to an extreme angle in a preferential direction whilemaintaining support and strength by retaining material that limitspivoting in other directions. In the example of FIGS. 1-3, the screwseat 108 includes a notch 112 (FIG. 3) that permits the screw 104 topivot preferentially into the notch 112. As best seen in FIG. 3, thescrew 104 is also able to swivel about the longitudinal axis 110 in ahorizontal plane transverse to the longitudinal axis 110 as the screwseat 108 rotates within the rod holder 106. This combination of verticalpivoting and horizontal swiveling allows the rod holder 106 to beswiveled to any desired position independently of the position of thenotch 112 and screw 104 to selectively orient the position of maximumscrew pivoting. Various mechanisms for achieving this motion aredetailed below.

FIGS. 4-8 illustrate the details of one embodiment of the pedicle screwassembly 100 of FIG. 1. The pedicle screw assembly 100 includes a screw104, a rod holder 106, a mounting in the form of a screw seat 108, a rodinsert 114, and a set screw 116.

The screw 104 includes an elongated shank 118 having a tip 120 at adistal end, a head 122 at a proximal end, and a longitudinal axis 124extending therebetween. A thread 126 spirals around the shank such thatthe screw 104 may be threaded into a bone. The head 122 may becylindrical, conical, elliptical, spherical, and/or any other suitableshape. In the illustrative example of FIG. 4, the head 122 is generallyspherical with a lower screw seat contacting portion 128 and an upperinsert contacting portion 130.

The rod holder 106 includes a generally cylindrical body 132 having alongitudinal passageway 134 extending through the body 132 along an axis136 from an upper or first opening 138 near a proximal end to a lower orsecond opening 140 near a distal end. The body 132 defines a screw seatcontacting surface 142 adjacent the lower opening 140. The screw seatcontacting surface 142 is preferably concave and spherical and has adiameter greater than the diameter of the lower opening 140. Atransverse passageway 144 extends through the body 132 transverse to theaxis 136 for receiving the rod 102 (FIG. 1). Preferably the transversepassageway 144 is open proximally to allow the rod 102 to be placed intothe rod holder 106 with a proximal to distal motion. Alternatively thetransverse passageway 144 may be closed proximally such that the rod 102must be inserted transversely through the rod holder 106. A screw thread146 spirals from the upper opening 138 distally into the rod holder body132.

The screw seat 108 has a generally cylindrical body 148 with a lower,rod holder contacting surface 150. The rod holder contacting surface 150is preferably convex and spherical such that it mates with the screwseat contacting surface 142 in relative pivoting relationship. Alongitudinal passageway 152 extends through the body 148 along an axis154 from an upper opening 156 near a proximal end to a lower opening 158near a distal end. The body 148 defines a screw head seating surface 160adjacent the lower opening 158. The screw head seating surface 160 ispreferably concave and spherical. A notch 162 extends radially outwardlyfrom the longitudinal passageway 152 and is sized to receive a portionof the screw shank 118. The notch 162 may extend only partway throughthe body 148 or it may extend completely through the body as shown inFIG. 4 and as will be discussed in more detail below.

The insert 114 has a generally cylindrical body 164 extending along alongitudinal axis 166 from an upper portion 168 near a proximal end to alower, screw head contacting surface 170 near a distal end. The screwhead contacting surface 170 preferably includes an axial hole 172defining an annular seat 174. A transverse passageway 176 extendsthrough the body 164 transverse to the axis 166 for receiving the rod102. Preferably the transverse passageway 176 is open proximally toallow the rod 102 to be placed into the insert 114 with a proximal todistal motion. Alternatively the transverse passageway 176 may be closedproximally such that the rod 102 must be inserted transversely throughthe insert 114. The bottom of the transverse passageway 176 defines arod contacting surface and is preferably concave and cylindrical.

The set screw 116 has a generally cylindrical body 178 about alongitudinal axis 180, a thread 182 spiraling around its exterior, and adriver engaging portion 184, in this example a multi-lobed opening. Theset screw 116 is threadably receivable in the upper opening 138 of therod holder 106.

FIGS. 5 and 6 illustrate a method of assembling the components of FIG.4. Referring to FIG. 5, the screw head 122 is inserted upwardly throughthe lower opening 140 of the rod holder 106. The screw seat 108 istipped sideways and inserted through the upper opening 138 of the rodholder 106 with the notch 162 directed toward the screw head 122. As thescrew seat 108 engages the screw seat contacting surface 142, the screwseat 108 is tipped upright so that the notch 162 slides under the screwhead 122 and receives the screw shank 118. Preferably the passageway 152and notch 162 are sized to fit closely around the screw shank 118 suchthat the screw 104 is only allowed to pivot in the direction of thenotch and not transverse to the direction of the notch. Alternatively,for example in the case where the notch 162 does not extend all the waythrough the screw seat 108, the screw seat 108 may be positioned in therod holder 106 and the screw 104 inserted through the upper opening 138of the rod holder 106 and into the screw seat 108. However, in thisalternative case, the passageway 152 through the screw seat would needto be enlarged enough to allow the screw thread 126 to pass.

Referring to FIG. 6, once the screw 104 and screw seat 108 arepositioned in the rod holder 106, the insert 114 is placed over thescrew 104 in preparation for receiving the rod 102. The screw 104, screwseat 108, and insert 114 may be assembled intraoperatively by thesurgical team or they may be preassembled. Preferably the components arepreassembled and locked in place to prevent disassembly in order tosimplify their use in surgery. In the illustrative embodiment of FIGS.4-8, the rod holder 106 includes a blind hole 186 defining a thin web188 of material that is pressed inwardly to stake the insert 114 in therod holder 106 to prevent disassembly.

During surgery, the screw 104 is driven into a bone, e.g. a pedicle, ata desired angle. The rod holder 106 is pivoted relative to the screw 104to a desired angle with the screw 104 in the notch 162 and the rodholder 106 is swiveled relative to the screw seat 108 to a desiredorientation to align the transverse passageway 144 with a desired rodorientation. The rod 102 is then placed into the transverse passageway144 and the set screw 116 is threaded into the rod holder 106 to pressthe rod 102, insert 114, screw 104, screw seat 108, and rod holder 106together to lock the construct in the desired position.

In the illustrative embodiment of FIGS. 4-8, the screw seat 108 andinsert 114 are shaped to have a gap 190 between them and the screw seat108 is relieved (as shown at 192 in FIG. 6) adjacent the screw shank 118such that the screw seat 108 can pivot relative to the screw seatcontacting surface 142 of the rod holder 106 and the screw shank 118 canpivot relative to the screw seat 108. This in effect produces a “doublethrow” action in which the screw 104 can pivot a first amount (FIG. 7)until the screw shank 118 abuts the screw seat 108 and the screw seat108 abuts the insert 114 in most directions and a farther amount (FIG.8) in the preferential direction of the notch 162 until it abuts the rodholder 106. The rod holder 106 may be notched to allow further pivotingin the preferred direction and/or the screw seat 108 may be extended toprotrude former below the rod holder 106 to provide more pivoting beforethe screw shank 118 abuts the rod holder 106.

In the embodiment of FIG. 9, there are no gaps and the screw 104 canonly pivot in the direction of the notch 162. In other words the screw104 is pivotally constrained in all directions except in the directionof the notch 162. This “single throw” arrangement advantageously keepsthe head 122 of the screw centered relative to the insert 114 forimproved locking when the insert 114 is pressed against the screw head122.

FIGS. 10-12 illustrate an alternative screw seat 200 that is generallyconfigured like, and operates like the screw seat 108 of FIGS. 4-8.Specifically, screw seat 200 differs from that of FIGS. 4-8, in that ithas an elongated screw head seating surface 260 that allows the screwhead 122 to slide along an arc and pivot at any position on the arc.Alternatively, the elongated screw head seating surface 260 may includea plurality of discrete head seating regions 261 allowing discreteranges (FIG. 12) of screw angulation by selectively engaging the screw104 with a preferred seating region. This may be advantageous inpermitting additional pivoting range to the screw 104. It may also beadvantageous in a “double throw” arrangement as shown in FIGS. 7-8 toallow the head 122 to slide relative to the seat 108 and stay centeredrelative to the insert 114 for improved locking.

FIGS. 13-15 illustrate the details of another embodiment of a pediclescrew assembly like that of FIG. 1. In this embodiment, the screw has atransverse head (described more fully below) that engages the screw seatin hinge pivoting relationship. The transverse head in combination withthe pivoting and swiveling aspects of the invention allow for a compactscrew assembly presenting a low profile. As best seen in FIG. 14, thescrew head has a small vertical height 316 relative to a largetransverse width 318 and the overall vertical dimension 320 of the rodholder and screw head assembly is small. The low profile nature of thepresent invention is advantageous because it allows the pedicle screwassembly to be used in situations where traditional “poliyaxial” screwsare not indicated because they cannot fit. The low profile nature of thepresent invention also provides aesthetic and comfort advantages byreducing the presence of protruding bumps under a patient's skin,especially in smaller and or thinner patients with less fleshy masssurrounding the screws. The transverse head arrangement of thisembodiment permits a low profile while simultaneously more positivelycapturing the head and increasing the mechanical strength of theassembly. The pedicle screw assembly 300 includes a screw seat 302, ascrew 304, an insert 306, a rod holder 308, a swivel ring 310, aretaining ring 312, and a set screw 314.

The screw seat 302 has a generally cylindrical body 324 defining aproximally facing shoulder 326, a rim 328, and an undercut 329 (FIG.14). A longitudinal passageway 330 extends through the body along anaxis 332 from an upper opening 334 near a proximal end to a loweropening near a distal end. The body defines a screw head contactingsurface 338 extending distally into the body 324. The screw headcontacting surface 338 may be cylindrical, conical, elliptical,spherical, and/or any other suitable shape. In the illustrative exampleof FIGS. 13-15, the screw head contacting surface 338 includes bilateralcylindrical depressions formed in the body on either side of thelongitudinal passageway 330 and aligned along an axis 340 transverse tothe longitudinal axis 332. A notch 342 extends outwardly from thelongitudinal passageway 330 and is sized to receive a portion of thescrew 304. The notch 342 may extend only partway through the body 324 orit may extend completely through the body 324 as shown in FIG. 13.

The screw 304 includes an elongated shank 350 having a tip 352 at adistal end, a head 354 at a proximal end, and a longitudinal axis 356extending therebetween. A thread 358 spirals around the shank 350 suchthat the screw 304 may be threaded into a bone. The head may becylindrical, conical, elliptical, spherical, and/or any other suitableshape to cooperatively engage head contacting surface 338. In theillustrative example of FIG. 13, the head is generally cylindrical andprojects outwardly transverse to the screw shank along an axis 360. Thescrew is generally “T”-shaped and the head 354 is sized to engage thescrew head contacting surface 338 of the screw seat 302 with the axes340, 360 coaxially aligned such that the screw may pivot about the axes340, 360 with the shank 350 moving in the longitudinal passageway 330and notch 342.

The insert 306 has a generally cylindrical body 364 extending along alongitudinal axis 366 from an upper portion 368 near a proximal end to alower, screw head contacting surface 370 near a distal end. A transversepassageway 372 extends through the body transverse to the axis 366 forreceiving the rod 102. Preferably the transverse passageway 372 is openproximally to allow the rod 102 to be placed into the insert 306 with aproximal to distal motion. Alternatively the transverse passageway 372may be closed proximally such that the rod 102 must be insertedtransversely through the insert 306. The bottom of the transversepassageway 372 defines a rod contacting surface 374 and is preferablyconcave and cylindrical. The body includes a longitudinal rib 362 thatengages a corresponding groove 363 (FIG. 14) in the rod holder 308 toorient the transverse passageway 372 relative to the rod holder 308.

The rod holder 308 includes a body 380 having a longitudinal passageway382 extending through the body 330 along an axis 384 from an upper orfirst opening 386 near a proximal end to a lower or second opening 388near a distal end. The lower opening 388 is sized to receive the insert306 and screw head 354. The body 380 defines a distally facing shoulder390, a rim 392, and an undercut 393 extending into the body 380 (FIG.14). A transverse passageway 394 extends through the body 380 transverseto the axis 384 for receiving the rod 102. Preferably the transversepassageway 394 is open proximally to allow the rod 102 to be placed intothe rod holder 308 with a proximal to distal motion. Alternatively thetransverse passageway 394 may be closed proximally such that the rod 102must be inserted transversely through the rod holder 308. A screw thread396 spirals from the upper opening 386 distally into the rod holder body380. The body 380 defines an enlarged cavity 398 for receiving theinsert 306. The cavity 398 defines an internal distally facing shoulder399 against which the upper portion 368 of the insert 306 abuts to trapthe insert 306 in the cavity 398 between the rod holder 308 and screwseat 302.

The swivel ring 310 includes a generally cylindrical body 400 having alongitudinal passageway 402 extending through the body 400 along an axis404 from an upper or first opening 406 near a proximal end to a lower orsecond opening 408 near a distal end and defining an inner surface 410.The swivel ring 310 has an outer diameter and an inner diameter. Theswivel ring 310 includes an internal annular groove 412 extending intothe body 400 from the inner surface 410 radially outwardly. The swivelring 310 is interrupted by a notch 414 so that the swivel ring 310 canbe elastically deformed to change the inner and outer diameters. Theinner diameter and annular groove 412 are sized to engage the rims andundercuts of the screw seat 302 and rod holder 308 as will be explainedfurther below.

The retaining ring 312 comprises a generally cylindrical hollow ringhaving an internal diameter sized to press lit around the swivel ring310.

The set screw 314 has a generally cylindrical body 420 about alongitudinal axis 424, a thread 426 spiraling around its exterior, and adriver engaging portion 428. The set screw 314 is threadably receivablein the upper opening 386 of the rod holder 308.

FIGS. 14 and 15 illustrate the pedicle screw assembly 300 of FIG. 13 incross section. To assemble the pedicle screw assembly 300, the screwhead 354 is seated in the screw seat 302. The insert 306 is placed inthe cavity 398 of the rod holder 308 and the top of the screw seat 302is abutted with the bottom of the rod holder 308. The swivel ring 310 issprung open so that it can be slipped over the rod holder 308 and screwseat 302. The swivel ring is snapped into place with the rims 328, 392of the screw seat 302 and rod holder 308 captured in the groove 412. Theretaining ring 312 is then pressed into place around the swivel ring 310to prevent the swivel ring 310 from springing open and releasing thescrew seat 304 and rod holder 308. The screw seat 302 and rod holder 308are free to rotate relative to one another about a longitudinal axis andthe screw 304 is free to pivot relative to the screw seat 302 about atransverse axis. The “T”-head configuration of the screw 304 and screwseat 302 creates a hinge joint between them constraining the screw 304and screw seat 302 to one degree of rotational freedom relative to oneanother. In the embodiment of FIGS. 13-15, the screw shank 350 abuts theside of the longitudinal passageway 330 to prevent the screw 304 frompivoting to the left in FIG. 15. The screw 304 can pivot freely to theright in FIG. 15 and into the notch 342 to an extreme pivot angle. Thepivot angle can be increases further by extending the screw seat 302further distally to deepen the notch 342 to receive more of the screw304. Pivot angles of 90 degrees or more are easily obtainable with sucha modification. Conversely, the shallow screw seat of FIGS. 13-15provide for a more compact, low profile assembly.

During surgery, the screw 304 is driven into a bone, e.g. a pedicle, ata desired angle. The rod holder 308 is pivoted relative to the screw 304to a desired angle with the screw 304 in fee notch 342 and the rodholder 308 is swiveled relative to the screw seat 302 to a desiredorientation to align the transverse passageway 394 with a desired rodorientation. The rod 102 is then placed into the transverse passageway394 and the set screw 314 is threaded into the rod holder 308 to pressthe rod 102, insert 306, screw 304, screw seat 302, and rod holder 308together to lock the construct in the desired position.

FIGS. 16-18 illustrate the details of another embodiment of a pediclescrew assembly 500 like that of FIG. 1. The pedicle screw assembly 500of FIGS. 16-18 is similar to that of FIGS. 13-15 in that it includes ascrew seat 502, a “T”-shaped screw 504, an insert 506, a rod holder 508,and a set screw 510. However, the pedicle screw assembly 500 of FIGS.16-18 differs from that of FIGS. 13-15 in that instead of having aswivel ring and retaining ring to capture and hold the screw seat 502and rod holder 508 together, the screw seat 502 and rod holder 508 snaptogether directly. The screw seat 502 is in the form of a lower shellhaving a rim 512 and an undercut 514 and the rod holder 508 is in theform of an upper shell having a rim 516 and an undercut 518 (FIG. 18).The screw seat 502 and rod holder 508 snap together with the rim of onefitting into the undercut of the other. The insert 506 of the embodimentof FIGS. 16-18 also differs from the insert 306 of the embodiment ofFIGS. 13-15. The insert 506 has a cylindrical concave lower surface 520shaped to receive the cylindrical head 522 of the screw 504 (FIG. 16).The insert 506 also has a cylindrical boss 524 (FIG. 17) that projectsupwardly through a central longitudinal passageway 526 into a transverserod receiving passageway 528. When a rod 102 is placed in the pediclescrew assembly 500 and the set screw 510 is tightened, the rod 102presses against the boss 524 which forces the insert 506 against thescrew head 522 to lock the construct in position. Note that theembodiment of FIGS. 16-18 is shown with a relatively deep screw seat 502and correspondingly deep screw receiving notch to permit high pivotangles.

One of the characteristics of the embodiments of FIGS. 13-18 is that thescrew and screw seat do not swivel about the longitudinal axis relativeto one another so that in order to orient the direction of preferentialscrew pivoting, e.g. the notch, relative to the bone, the screw isthreaded into or out of the bone. Generally a preferred orientation ofthe notch can be achieved within a half turn in either direction so thatthe change in screw depth is minimal. FIGS. 19-20 illustrate a screwassembly 600 that can be substituted for the screw in the embodiments ofFIGS. 13-18 to permit adjustment of the direction of preferential screwpivoting independent of screw depth. The screw assembly 600 includes ascrew 602, a separate modular “T”-head 604, and a screw seat 603. Thescrew 602 includes an elongated shank 605 having a tip 606 at a distalend, a head 608 at a proximal end, and a longitudinal axis 610 extendingtherebetween. A thread 612 spirals around the shank 605 such that thescrew 602 may be threaded into a bone. The “T”-head 604 includes agenerally cylindrical body 614 oriented along a head axis 616 and apassageway 618 through the body 614 transverse to the head axis 616. The“T”-head 604 is preferably an assembly of two half heads that areassembled to a reduced portion of the shank 605 transverse to thelongitudinal axis 610. By making the “T”-head 604 in two halves, thescrew head 608 and “T”-head 604 can be made more compact since thepassageway and screw head 608 can have a smaller diameter than thethread 612. However, a one-piece “T”-head 604 is within the scope of theinvention with the diameter of the passageway 618 and head 608 sizedaccordingly. A countersunk seat 622 is formed coaxially with thepassageway 618 to receive the screw head 608. A lower surface 624 of thescrew head 608 abuts the seat 622 to prevent the screw 602 from passingthrough the “T”-head 604. With the screw 602 received in the passageway618 of the “T”-head 604, the assembly 600 of FIG. 19 may be substitutedfor the “T”-shaped screws 304, 504 of FIGS. 13-17 to permit the screwseat 302, 502 (along with the “T”-head 604) to be rotated about the axis610 without the need to rotate the screw shank 605 relative to the bone.Thus, the orientation of preferential screw pivoting may be adjustedwithout changing the depth of the screw 602 in the bone. The “T”-head ofFIGS. 19-20 optionally includes an annular groove 626 formed about thehead axis 616 on each side of the body 614. As best seen in FIG. 20, thegroove 626 captures a portion 628 of the screw seat 605 on each side toprevent the screw seat 605 from splaying open when forces are applied tothe pedicle screw assembly 600.

FIGS. 21-23 illustrate the details of another embodiment of a pediclescrew assembly 700 like that of FIG. 1. The embodiment of FIGS. 21-23includes a screw seat 702, a “T”-shaped screw assembly 704, a lockingring 706, a rod holder 708, and a set screw 710. The assembly of thescrew seat 702 and rod holder 708 is similar to the embodiment of FIG.16 except that the screw seat 702 and rod holder 708 of FIG. 21 arelocked with a locking ring 706 rather than snapping directly together.The screw seat 702 includes a groove 712 and the rod holder 708 includesa groove 714 each sized to receive a portion of the locking ring 706.The locking ring 706 includes a notch 716 allowing it to be elasticallyexpanded and contracted. The locking ring 706 is first assembled ontoone of the components, e.g. it can be snapped into the groove 712 in thescrew seat 702. The rod holder 708 is then pressed into the screw seat702 causing the locking ring 706 to expand until the grooves 712, 714are aligned and the locking ring 706 contracts to reside partially ineach groove 712, 714 and lock the rod holder 708 and screw seat 702together for relative rotation.

The “T”-shaped screw assembly 704 of FIGS. 21-23 permits orientation ofthe preferential screw pivot direction without changing the depth of thescrew assembly 704 in the bone similar to the embodiment of FIG. 19-20.However, in the embodiment of FIGS. 21-23 the “T”-shaped screw assembly704 includes a pin 718 inserted transversely through a passageway 720 ina head 722 of a screw 723. The passageway 720 is rotationally enlargedabout the longitudinal axis 724 so that pin 718 and screw 723 are ableto rotate relative to one another about the longitudinal axis 724. Thus,when the pin 718 is seated in the screw seat 702, the screw seat 702 andpin 718 can rotate about the screw 723.

The embodiment of FIGS. 21-23 also differs from the other embodiments inthat there is no insert and the rod 102 (not shown in FIGS. 21-23) bearsdirectly on the screw head 722.

FIGS. 24-25 illustrate the details of another embodiment of a pediclescrew assembly similar to the previous embodiments. The pedicle screwassembly 800 includes a screw seat 802, a “T”-shaped screw 804, aninsert 806, a rod holder 808, a retaining ring 810, and a set screw (notshown). The rod holder 808 includes a plurality of distally extendingtabs 812 having inwardly directed lips 814. The screw seat 802 includesan annular groove 818 able to receive the lips in snap fittingrelationship. The rod holder 808 attaches to the screw seat 802 bypressing the tabs 812 over the screw seat 802 causing the tabs 812 toflex outwardly until the lips 814 engage the groove 818 allowing thetabs to snap inwardly. The retaining ring 810 is pressed onto the rodholder 808 so that it surrounds the tabs 812 and prevents them fromflexing outwardly and releasing the screw seat 802.

FIGS. 26-27 illustrate the details of another embodiment of a pediclescrew assembly similar to the previous embodiments. The pedicle screwassembly 850 includes a screw seat 852, a “T”-shaped screw 854, a rodholder 856, and a set screw (not shown). One or more plates 858 areprovided to attach the rod holder 856 to the screw seat 852. Each platesincludes a distally extending portion 860 having an inwardly projectinglip 862. The screw seat 852 includes an annular groove 864 able toreceive the lips 862. The plate is attached to the rod holder 856 usinga suitable fastening mechanism such as a screw, clip, adhesive, welding,soldering, and or other suitable fastening mechanism. In theillustrative example, two plates 858 are inset into notches 866 formedin opposite sides of the rod holder 856 and screws 868 extend throughthe plates 858 and thread into the rod holder 856 to attach them to therod holder 856.

Although examples of a hone fastener assembly and its use have beendescribed and illustrated in detail, it is to be understood that thesame is intended by way of illustration and example only and is not tobe taken by way of limitation. The invention has been illustrated in theform of a pedicle screw assembly for use in assembling stabilizingconstructs to connect vertebrae of the human spine. However, the bonefastener assembly may be configured with other kinds of fasteners andconnecting members to assemble other kinds of constructs to stabilizebones and bone fragments at any location in the body. Accordingly,variations in and modifications to the bone fastener assembly and itsuse will be apparent to those of ordinary skill in the art. The variousillustrative embodiments illustrate alternative configurations ofvarious component parts such as screw seats, screws, pivot mechanisms,swivel mechanisms, and inserts among others. In most cases, and as willbe readily understood by one skilled in the art, the alternativeconfiguration of a component part in one embodiment may be substitutedfor a similar component part in another embodiment. For example, thescrew seat shown in the embodiment of FIGS. 1-8 may be readily modifiedwith a cylindrical seat to be used with any of the “T”-head screws shownin the embodiments of FIGS. 13-27. Likewise, the various mechanismsillustrated for attaching the screw seat to the rod holder may beinterchanged. Furthermore, throughout the exemplary embodiments, wherecomponent part mating relationships are illustrated, the gender of thecomponent parts may be reversed as is known in the art within the scopeof the invention. The following claims are intended to cover all suchmodifications and equivalents.

What is claimed is:
 1. A bone fastener assembly for connecting a bone toa spinal rod, comprising: a rod holder, having a rod holder axis, a rodreceiving passageway extending through the rod holder transverse to therod holder axis for receiving said spinal rod; a fastener seat mountedto the rod holder for rotation about the rod holder axis, the fastenerseat comprising a first end and a second end opposite the first end witha passageway traversing from the first end to the second end, and anotch in communication with the passageway; and a bone fastener havingan elongated shank including a bone engaging portion at a first end, ahead at a second end, and a fastener axis extending therebetween, thehead being elongated in substantially a single direction transverse tothe fastener axis such that the bone fastener is generally “T”-shaped,the head engaging the fastener seat in pivoting relationship such thatthe bone fastener is able to pivot in at least one vertical planecontaining a seat axis to vary an angle between the bone fastener andthe fastener seat such that the bone fastener pivots; wherein thefastener seat comprises an outer edge and the notch extends radiallyoutwardly from the passageway at least part way to the outer edge, thefastener being able to pivot in only one direction from a first positionin which the fastener axis and the seat axis are parallel to a secondposition in which the fastener axis and seat axis are transverse, thenotch receiving a portion of the fastener when the fastener is in thesecond position.
 2. The bone fastener assembly of claim 1 wherein thefastener is able to pivot in only one vertical plane containing the seataxis relative to the fastener seat to vary the angle between the bonefastener and the fastener seat.
 3. The bone fastener assembly of claim 1wherein the head comprises a cylindrical surface and the fastener seatcomprises a complimentary mating cylindrical surface.
 4. The bonefastener assembly of claim 1 wherein the fastener seat comprises anannular rim and the rod bolder comprises an annular rim, the bonefastener assembly further comprising a swivel ring having an internaldiameter and an annular groove formed about the internal diametersimultaneously engageable with the annular rims of the rod holder andthe fastener seat.
 5. The bone fastener assembly of claim 4 wherein thering is interrupted such that it can be opened to receive the annularrims, the bone fastener assembly further comprising a retaining ringreceivable around the swivel ring to prevent the swivel ring fromopening.
 6. The bone fastener assembly of claim 1 wherein the fastenerseat comprises a rim and an undercut and the rod holder comprises a rimand an undercut, the fastener seat and rod holder being engageable withone another in snap-fitting relationship with the rim of one fittinginto the undercut of the other.
 7. The bone fastener assembly of claim 6wherein the rim of at least one of the fastener seat and rod holder isinterrupted and defines a plurality of radially flexible tabs and thebone fastener assembly further comprises a retaining ring receivablearound the tabs.
 8. The bone fastener assembly of claim 1 wherein eachof the fastener seat and the rod holder comprises a groove and thefastener seat and rod holder telescope together with the groovesaligned, the bone fastener assembly further comprising a locking ringsized to seat simultaneously in both grooves and lock the fastener seatand rod holder together.
 9. The bone fastener assembly of claim 1further comprising at least one plate mountable to the rod holder andengageable with the fastener seat.
 10. The bone fastener assembly ofclaim 9 wherein the rod holder comprises an outer surface and the atleast one plate is inset into the outer surface.
 11. The bone fastenerassembly of claim 9 wherein the plate is mounted to the rod holder by atleast one screw.
 12. The bone fastener assembly of claim 9 wherein theplate comprises a lip and the fastener seat comprises a groove, the lipbeing engageable with the groove to retain the fastener seat relative tothe rod holder.
 13. The bone fastener assembly of claim 1 wherein thehead comprises a separate member mounted to the fastener for rotationabout the fastener axis.
 14. The bone fastener assembly of claim 13wherein the separate member comprises a plurality of separate membersassembled to the fastener transverse to the fastener axis.
 15. The bonefastener assembly of claim 13 wherein the fastener comprises atransverse passageway formed through the fastener transverse to thefastener axis and the separate member comprises an elongated memberinserted through the transverse passageway, the transverse passagewaybeing rotationally enlarged about the fastener axis such that elongatedmember is rotatable about the fastener axis.
 16. The bone fastenerassembly of claim 1 wherein the head comprises first and second ends andan annular groove formed about each of the first and second ends, eachannular groove receiving a portion of the fastener seat on opposingsides of the fastener seat.
 17. A bone fastener assembly for connectinga bone to a spinal rod, comprising: a rod holder having a longitudinalaxis and a rod receiving passageway extending through the rod holdertransverse to the longitudinal axis, the rod receiving passagewayadapted to receive said spinal rod; a fastener seat mounted to the rodholder for rotation about the longitudinal axis, the fastener seatcomprising a passageway, a substantially planar proximal seat surface,and a substantially planar distal seat surface, the passageway extendingfrom the substantially planar proximal seat surface to the substantiallyplanar distal seat surface along the longitudinal axis and a notch, thefastener seat comprising bilateral depressions formed in thesubstantially planar proximal seat surface on opposite sides of thenotch; and a bone fastener having an elongated shank including a boneengaging portion at a first end, a head at a second end, and a fasteneraxis extending therebetween, the head comprising bilateral extensions tocooperatively engage the bilateral depressions in the fastener seat suchthat, the bilateral extensions of the head engage the bilateraldepressions in the fastener seat in a hinged relationship such that thebone fastener may pivot in the notch to vary an angle between the bonefastener and the fastener seat, wherein the bone fastener pivots to agreater angle in a direction of the notch.
 18. The bone fastenerassembly of claim 17 wherein the head of the bone fastener iscylindrical and forms a generally “T” shape.
 19. The bone fastenerassembly of claim 17 further comprising: a swivel ring comprising anannular groove, wherein: the rod holder has a proximal end and a distalend, the distal end of the rod holder comprising a shoulder, a rim, andan undercut; the fastener seat has a proximal end and a distal end, theproximal end of the fastener seat comprising a shoulder, a rim, and anundercut, such that the shoulders, rims, and undercuts fit within theannular groove to rotatably couple the rod holder and the fastener seat.20. The bone fastener assembly of claim 19 wherein the head of the bonefastener comprises a height and a width wherein the height is less thanthe width.
 21. The bone fastener assembly of claim 19 further comprisinga retaining ring having a retaining ring passageway to fit about theswivel ring.
 22. The bone fastener assembly of claim 17, wherein thebilateral depressions have a first end and a second end opposite thefirst end and a length from the first end to the second end is less thanan outside width of the rod holder.